Functional and Objective Audiovestibular Evaluation of Children With Apparent Semicircular Canal Dehiscence–A Case Series in a Pediatric Vestibular Center

Soumit Dasgupta,Sudhira Asanka Bandara Ratnayake

doi:10.3389/fneur.2019.00306

Soumit Dasgupta, Sudhira Asanka Bandara Ratnayake

Open Access

https://doi.org/10.3389/fneur.2019.00306

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Abstract

Semicircular canal dehiscence is a bony abnormality in the otic capsule especially involving the superior semicircular canal. Since its identification in 1998, there is significant research regarding the pathology in the adult population. This condition generates a third window effect that is well–described in the literature. However, the entity is rare in the pediatric population with limited research. Difficulties encountered in children are obtaining a direct history that is essential for the diagnosis followed by neurovestibular tests that may be difficult to perform. This study presents observations regarding different clinical and diagnostic aspects of semicircular canal dehiscences in children as a retrospective audit in a tertiary pediatric vestibular center. Of 580 children assessed in a 30 months period undergoing comprehensive functional and objective audiovestibular assessment, 13 children (2.2%) were detected to possess radiological semicircular canal dehiscences (high resolution computed tomography scans at 0.625 mm slices reformatted in the axial, coronal and sagittal planes). The right superior semicircular canal was most commonly affected (66.6%). There were 4 bilateral semicircular canal dehiscences. Clinical suspicion of the condition was raised with reliable surrogate history from carers or from older children (100%), a mixed or conductive hearing loss (80% of hearing losses) in the presence of normal impedance audiometry (92.3%), normal transient otoacoustic emissions (84.6%) on the side of the dehiscence and the presence of replicable pathological saccades in the video head impulse test (76.9%). Disequilibrium symptoms and typical third window symptoms were absent or difficult to elicit in children (46.15 and 30.76% respectively). Only 3 (0.5%) fulfilled the adult criteria of a superior semicircular canal dehiscence syndrome. The abnormal video head impulse test characterized by pathological saccades may affect other non-dehisced ipsilateral canals. Semicircular canal dehiscences are rare in children but may be considered as an etiology for hearing losses and imbalance. Children with semicircular canal dehiscence may present differently from the classical superior semicircular canal dehiscence syndrome found in adults.

Highlights

The pathological entity of superior semicircular canal dehiscence (SSCD) since its first description by Minor [1] has seen immense interest and research
Described in patients with sound or pressure induced vertigo and nystagmus (Tullio’s and Hennebert’s phenomenon) with symptoms of chronic disequilibrium, the clinical features that subsequently came into light included oscillopsia, auditory features including conductive hearing loss, autophony, conductive dysacusis including gaze evoked tinnitus, pulsatile tinnitus, low frequency hearing loss, phonophobia, and aural fullness [2]
The pathological third window shunts away a proportion of the sound energy delivered at the stapes footplate-oval window interface and from the cochlea resulting in abnormally elevated air conduction thresholds in pure tone audiometry

Summary

Introduction

The pathological entity of superior semicircular canal dehiscence (SSCD) since its first description by Minor [1] has seen immense interest and research. The pathophysiology of the auditory features of SSCD can be attributed to the pathological presence of a third window in addition to the natural two windows for maintaining integrity of inner ear sound conduction. The pathological third window shunts away a proportion of the sound energy delivered at the stapes footplate-oval window interface and from the cochlea resulting in abnormally elevated air conduction thresholds in pure tone audiometry. The same mobile third window lowers the impedance or pressure difference of the cochlear traveling wave between the scala vestibuli and the scala tympani in the inner ear by allowing a new path for the sound to enter the inner ear thereby generating enhanced bone conduction thresholds in bone conducted pure tone audiometry [4]. Other conditions in the otic capsule generating a similar third window effect are posterior and lateral semicircular canal dehiscences, enlarged vestibular aqueducts, the X linked gusher syndrome, facial nerve canal dehiscences, dilated bony internal auditory meatus, and dehiscent carotid canals

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